NEW DELHI: An Indian court has convicted a human rights activist of aiding communist rebels in eastern India and sentenced him to life in prison, his attorney said Saturday. Dr. Binayak Sen, a 60-year-old physician and outspoken government critic, has worked in tribal villages and repeatedly tried to rally people to fight for their rights, often invoking the ire of authorities. On Friday, Judge B.P. Verma found Sen and two others guilty of sedition and sentenced them to life, according to attorney Amit Banerjee. However, he acquitted the three of the charge of waging war against the state, which is punishable by death, Banerjee said. “I will appeal the verdict in a higher court next week,” Banerjee told The Associated Press. Amnesty International said Sen's conviction violated international fair trial standards and would intimidate other human rights activists who provide a peaceful outlet for people's grievances. Sam Zarifi, the rights group's Asia-Pacific director, demanded that Indian authorities “immediately drop these politically motivated charges against Dr. Sen and release him.” “Dr. Sen, who is considered a prisoner of conscience by Amnesty International, was convicted under laws that are impermissibly vague and fall well short of international standards for criminal prosecution,” Zarifi said in a statement. The trial lasted three and a half years and Sen spent 22 months in prison before being granted bail by the Supreme Court last year. He surrendered to the court after Friday's verdict and was taken by police to a prison in Raipur, the capital of Chhattisgarh state, where he will serve his sentence. The charges against Sen stem from visits he made to the same prison in Raipur to treat rebels and other prisoners. Authorities say he used those visits to pass notes between jailed communist rebel leaders and their compatriots in the field. The two others convicted in the case were Narayan Sanyal, a Maoist, whom Sen used to meet in the prison, and a Calcutta-based trader, Piyush Guha, who prosecutors said carried Sen's messages to the Maoist rebels. Sen has insisted he only provided medical treatment during his visits. Passing notes, he maintains, would have been impossible because his visits were closely supervised by prison guards, attorney Banerjee said Saturday. Rights groups have been supporting Sen's case. In 2008, a group of 22 Nobel laureates - ranging from medicine winners to economics honorees - sent a letter to India's president and prime minister expressing their concerns about the case against Sen, saying he appeared to have been jailed for “exercising his fundamental human rights.” Sen was awarded the 2008 Jonathan Mann Award for global health and human rights.